In the practice of sewing with machines, a reciprocating needle is driven downwardly to pull thread from a spool and to form a loop beneath the material to be stitched. A bobbin, containing a second supply of thread, is then moved to pass through the loop. The needle is then driven upwardly whereby the needle thread pulls the loop along with the bobbin thread, to form a lock stitch in the material. This sequencing of the needle and the bobbin, along with their threads, is repeated in a continuing cycle of operation to form a line of stitching in the material.
During the sewing operation, the needle thread extends between the spool and the needle, passing through guides, tensioning devices and the eye of a reciprocating take-up lever so as to provide the necessary forces on the needle thread. The tensioning devices provide resistive forces to preclude excessive lengths of thread from being pulled from the spool during the downward movement of the needle. The take-up lever retracts the needle thread as the needle and its thread begin to pull the bobbin thread upwardly to thereby tighten both threads and thus form a tight lock stitch. Proper stitch formation requires precise adjustment of the tensioning devices and proper sequencing of the take-up lever with the movement of the needle and bobbin.
Even when the tensioning devices and take-up lever are properly adjusted and sequenced, limitations are inherent in all known sewing machines. For example, sewing machines traditionally utilize needle thread spools supporting thread of virtually limitless amount. The thread of the bobbin, because no technique has been devised for conveniently retracting a needle loop sufficiently to tighten the stitch-forming threads following passage of an enlarged bobbin through an enlarged loop. Longer take-up levers have been tried to effect the longer needle thread retraction necessitated by the use of enlarged bobbins. Unfortunately, such longer arms induce extraneous vibrations into the machines and thus cause undesirable, irregular stitches. As a result, enlarged bobbins are not used and an operator must, therefore, periodically stop sewing to replenish the thread of smaller bobbins, an inefficient digression from the sewing process.
Various devices have been developed and utilized for controlling the needle thread of sewing machines. U.S. Pat. No. 345,581 to Fleharty; U.S. Pat. No. 1,536,579 to Groebli; and U.S. Pat. No. 3,312,185 to Chezaud et al all relate to controlling needle thread through tensioning devices which are intermittent, variable or braked. In addition, U.S. Pat. No. 2,191,046 to Tiesler and U.S. Pat. No. 2,652,017 to Hohmann relate to take-up levers in combination with tensioning mechanisms for controlling needle threads in manners which are improvements over previously known mechanisms. None, however, is adequate to preclude precise and periodic adjustments and none is adequate to allow the use of enlarged bobbins required for supporting large amounts of thread.
As illustrated by the great number of prior patents, efforts are continuously being made in an attempt to more efficiently and conveniently sew with machines. None of these prior art efforts, however, suggests the present inventive method or combination of elements for sewing with rewound needle thread as disclosed and claimed herein. The devices and methods of the prior disclosures do not provide for the superior, consistent and convenient formation of tight stitches time after time while utilizing enlarged bobbins as with the method and apparatus of the present invention. The present invention achieves its purposes, objectives and advantages over the prior art through new, useful and unobvious apparatus and method steps which consistently and conveniently insure high quality stitches through the use of a minimum number of functioning parts, at a reduction in cost, and through the utilization of only readily available materials and conventional components.
These objects and advantages should be construed as merely illustrative of some of the more prominent features and applications of the present invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other objects and advantages as well as a fuller understanding of the invention may be had by referring to the summary of the invention and detailed description of the preferred embodiments of the invention in addition to the scope of the invention as defined by the claims taken in conjunction with the accompanying drawings.